(1) Field of the Invention
The present invention relates to a sound environment simulator which enables one to experience a computer simulation of sound performance when modeling acoustic affects in a listening room, a concert hall or the like, and to a method of analyzing spatial acoustic characteristics of a sound space.
(2) Description of the Related Art
Rapid advancement in the field of audio-visual technology makes it possible to supply high-quality music and images to individual homes. In particular, what has been attracting people's interest is a technique, a so-called "home theater", by which one can enjoy a movie or music at home as if he were in a movie theater or a concert hall. To enjoy the home theater, it is desirable to have a room where acoustic affects and sound insulation effects are well taken into account. However, in most of the cases, people enjoy movies and music in their living rooms where a variety of furniture and household appliances are installed. Thus, nowadays, not only the appearance and the feeling of being comfortable, but also the acoustic affects and insulation effects are important elements when designing for living rooms.
Conventionally, data related to acoustic characteristics are evaluated for modeling acoustic affects: they are computed by either experimental or analytical method and then fed back to design specifications.
In the experimental method, a model room is constructed, and an impulse response is measured directly to compute the acoustic characteristics data of the model room. However, the costs both for building materials and labor do not allow its application to individual house construction.
Whereas in the analytical method, the acoustic characteristics data are computed by a computer as it simulates a three dimensional sound field. This method has been widely used in recent years. Because the resulting data reliably correspond to various input conditions, become a reliable source for further analysis, and facilitate further processing and feedback to the design specifications.
Data necessary for simulating the three dimensional sound field are computed either by a numerical analysis or a geometric analysis based on theory of acoustics: sound waves are taken into account in the former, whereas they are not in the latter.
A finite element method(FEM) and a boundary element method(BEM) are typically used in the numerical analysis. In both the methods, the computer computes acoustic intrinsic modes or pressure distribution of a sound by solving a dominance equation of a stationary sound field, or namely Helmholtz's equation. Taking the sound waves into account makes it possible to analyze diffraction and interference of the sound; however, it does not allow the computation of a non-stationary value such as an echotime pattern. In particular, to compute the echotime pattern of a high frequency sound, a myriad number of lattices are involved, so that not only it takes a relatively long time period, but also the amount thereof exceeds a conventional memory capacity. For this reason, the numerical analysis has not been applied to practical applications.
On the other hand, in the geometric analysis based on the theory of acoustics, methods using sound rays or virtual images are typically used on the premise that the sound rays are reflected geometrically from walls. These methods are practical; for the memory capacity does not limit the amount of the computation. However, this analysis does not guarantee accuracy in all cases. For example, the resulting data may not be accurate when simulating the sound field with a low frequency sound in a room where a wave length is longer than its size. Because given these circumstances, the sound rays fail to reflect in accordance with the premise.
In addition, a reverberation time, which is a critical element to compute the acoustic characteristics data, is approximated by Sabine's or Eyring's equation to minimize the amount of computation for the sound ray tracing. Such an approximation causes an computation error when this analysis is applied to a space where a variety of household appliances are to be installed or whose shape is complex.
Another type of sound environment simulator has been developed in recent years. This type of simulator simulates a sound field by reproducing a sound in accordance with the acoustic characteristics data, so that one can hear the reproduced sound. In a broad sense, the sound environment simulator includes a model room where one can listen to a sound reproduced over speakers installed therein. However, this type of simulator is not applicable for individual house construction.
Accordingly, a sound environment simulator, disclosed in U.S. Pat. No. 4,731,848, was proposed. This simulator is designed to reproduce a sound over a headphone with reverberation effects. More precisely, an input audio signal is branched and the branched signal is inputted into a delay circuit. Then, the delay circuit delays the output of the branched signal for latency comparable to the time difference of the reflected sound to produce a reverberant signal. Subsequently, the original input audio signal and reverberant signal are composited to generate an output signal which is transduced into a sound. However, the sound reproduced in this way may give an impression to a listener that it does not sound realistic; for the sounds of higher order reflections (i.e. the sounds reflected for a number of times) are discarded.
Moreover, this type of simulator does not reproduce the sound immediately. This is because index data such as locations of a virtual sound source and the listener are inputted manually each time they move. Furthermore, the shape of a space selected as a model environment is limited.